1. Field of the Invention
This invention relates to ceramic capacitors and more particularly, to dielectric ceramic compositions suitable for fabrication of temperature compensating ceramic capacitors.
2. Description of the Prior Art
As is well known in the art, dielectric ceramic compositions are used as temperature compensating ceramic capacitors. The ceramic compositions for these purposes should preferable have a wide temperature characteristic of specific inductive capacity of from 0 to -280 and a high specific inductive capaciy of, for example, 115 while keeping the constant characteristic values. Typical of such ceramic compositions is a composition, as described in Japanese Patent Publication No. 55-25690. This composition comprises 5 to 25 mole % of BaTio.sub.3, 3 to 15 mole % of Bi.sub.2 O.sub.3, 55 to 70 mole % of TiO.sub.2, and 10 to 20 mole % of La.sub.2 O.sub.3 in a total amount of 100 mole %, to which at least one oxide selected from Y.sub.2 O.sub.3, Gd.sub.2 O.sub.3 and Nd.sub.2 O.sub.3 is added in an amount of 4 to 20 wt % of the above composition.
The quality factor, Q, of this dielectric ceramic composition is below 6300 in a maximum and approximately 5600 on average when a dielectric layer of the ceramic capacitor is about 0.85 mm.
The electrostatic capacitance of a capacitor is proportional to the square of a diameter of a counter electrode and is inversely proportional to the thickness. If it is intended to miniaturize a capacitor, the thickness of the dielectric ceramic has to be reduced by the square of a decrement in diameter of the counter electrode. However, when the thickness of the dielectric ceramic is reduced, the Q value also decreases substantially in proportion to the reduction of the thickness.
For the miniaturization of ceramic capacitors, there is a demand of dielectric ceramic composition which can yield higher Q values than known compositions.